Children exposed to multiple CT scans could be up to three times likelier to contract cancer of the blood, brain or bone marrow later in life, according to research published on Wednesday.

Writing in The Lancet medical journal, a team of scientists in Canada, Britain and the United States said the cancer risk, in absolute terms, appears to be small.

But they appealed for radiation doses from CT scans to be kept at a minimum and for alternatives to be used where appropriate. The researchers claimed their study was the first to provide direct evidence of a link between exposure from CT radiation in childhood and later cancer risk.